I am using FCPX and I have a matte and then a key. When I apply the matte all is good, but then when I have the key as well, the line where the matte ends shows up as this dark line and I can't figure out how to get rid of it.

Can you send a frame of that green screen to me?
I def think you can do it.
You just need to garbage matte that faded area.
Why do you have that weird green screen dark area anyway?
Was it part of the design?